1. Field of the Invention
The present invention relates to a diaphragm unit and a suspension.
2. Description of Related Art
A motorcycle in a related art has a suspension from a standpoint of riding comfort and so on. FIG. 7 is a view showing a vertical cross section of a suspension 200 provided on a rear-wheel side of the motorcycle in the related art.
The suspension 200 in the related art includes a cylinder 210 attached to a vehicle body side and a piston rod 220 attached to the axle side and slidably inserted into an oil chamber 216 of the cylinder 210 as shown in FIG. 7. The suspension 200 further includes a coil spring 230 provided in outer peripheries of the cylinder 210 and the piston rod 220.
The cylinder 210 has a double tube structure including an outer cylinder 210a and an inner cylinder 210b, having a vehicle body side mounting member 211 above the outer cylinder 210a. A piston 222 fixed by a nut 221 is provided on an upper side of the piston rod 220, and an axle side mounting member 223 is provided on a lower side thereof.
A spring load adjustment nut 231 is arranged in the outer periphery of the cylinder 210, and a spring bearing 232 supported by the spring load adjustment nut 231. A spring bearing 234 is provided on an upper side of the axle side mounting member 223. In an outer side portion of the spring bearing 234, a spring bearing guide 233 is provided. The coil spring 230 is provided between the spring bearing 232 and the spring bearing guide 233.
A lower part of the cylinder 210 is opened, and a rod guide 212 through which the piston rod 220 pierces is provided in an opening thereof as shown in FIG. 7. The rod guide 212 has an annular shape and provided at an inner peripheral portion of the cylinder 210 in a liquid tight manner. An oil seal 213 is provided at an inner peripheral portion of the rod guide 212, which allows the piston rod 220 to slide freely in a liquid tight manner.
An end plate 214 is provided in the opening of the cylinder 210 which is under the rod guide 212. An upper end surface of the end plate 214 abuts on the rod guide 212. The end plate 214 has an annular shape and is provided in the inner peripheral portion of the cylinder 210 in the liquid tight manner. A dust seal 215 is provided at an inner peripheral portion of the end plate 214, which prevents intrusion of dust.
A damping force generating apparatus 240 and a reservoir 241 communicating to the damping force generating apparatus 240 are arranged in series on an upper portion of the outer cylinder 210a where the vehicle body side mounting member 211 is formed. The damping force generating apparatus 240 communicates to a piston side oil chamber 216a and a rod side oil chamber 216b inside the cylinder 210. The damping force generating apparatus 240 adjusts a compression side damping force and an extension side damping force. The reservoir 241 compensates volume of the piston rod 220 moving forward and backward in the oil chamber of the cylinder 210 (including volume increased by temperature expansion of oil).
In the suspension 200 in the related art having the above structure, the piston 222 moves forward and backward in the oil chamber of the cylinder 210, thereby absorbing and damping vibration inputted from a road surface when a vehicle runs. Also, a spring force of the coil spring 230 absorbs an impact force received by the vehicle from the road surface and reduces transmission of vibration to the vehicle.
As a spring constant in the coil spring 230 is fixed in the suspension 200 in the related art, it is necessary to replace the coil spring 230 with one having a different spring constant for changing a reaction force. It is also necessary to remove the suspension 200 from a vehicle body (not shown) at the time of replacing the coil spring 230, the work is complicated.
Here, as structure of the suspension, there is air spring structure in which a diaphragm is provided around part of the cylinder and the piston rod 220 to form an air chamber and the reaction force is generated by using a pressure of the air inside the air chamber.
When the coil spring structure is compared with the air spring structure, a load of the coil spring 230 is heavier than members forming the air chamber, therefore, an inertia force and a bending load acting on the suspension are higher in the coil spring structure than in the air spring structure. Accordingly, actuation performance of a stroke in the coil spring structure is worse than in the air spring structure. Therefore, the air spring structure is preferable to the coil spring structure for adjusting the reaction force easily and for improving the actuation performance of the stroke.